Foil gauge



2 Sheets-Sheet l Jan.l6, 1942. c. M. HATHAWAY FOIL GAUGE Filed July 9, 1958 Inventor". Claude M. Hathawa by IVW Hi s Att oT-n ey. y

Jan. 6, 1942. g M. HATHAWAY 2,269,152

Inventor: Claude M. Hathaway,

by W

n1s Attorney.

` Patented Jan. 6, 19742 FOIL GAUGE Claude M. Hathaway, Niskayuna, N. Y., asslgnor to General 4Electric Company, a corporation of New York Application July 9, 1938, Serial No. 218,476

9 Claims.

This application is a continuation-impart .of

February 19, 1937, and S. N. 198,337, led March 26. 1938, both assigned to the same assignee as the present application.

My invention relates to electric gauges Aand concerns particularly thickness gauges for foil and metallic sheets.

It is an object of my invention to provide a simple, sturdy, reliable, compact. and easily operated thickness gauge which is adapted to measure thickness of foil or sheets continuously, if desired, at any speed, and which is unatfected by variations in position of the material being gauged.

It is a further object of my invention to provide apparatus which is adapted for gauging material varying widely in thickness, in which a relatively large gauging gap may be employed for easily accommodating the material to be gauged, and in which the measurement is relatively unaffected by variations in the size of the gap for receiving the material being gauged.

Still another object of my invention is to provide apparatus for automatically controlling the thickness of foil or sheet material during process of manufacture.

It is also an object of my invention to provide gauging apparatus-having zero and sensitivity adjustments with the zero adjustment independent of the sensitivity adjustment and independent of fluctuations in supply voltage.

VAdditional objects of my invention are the measurement of thickness of metallic wire and the measurement of conductivity or of purity'of metallic sheets or wires of uniform thickness.

It is also an object of my invention to provide an improved form of gauges of the movable spindletype for measuring mechanical dimensions.

Other and further objects and advantages will become apparent as the description proceeds.

In carrying out my invention in its preferred form, I provide na pair of jaws carrying cooperating parts of an electric gauge having a 'gap through which'the material to be gauged may be the passed. The electric .gauge includes a laminated' magnetic core with windings in inductive relation to the core. The windings include an exciting winding energized by audio-frequency current and detecting windings which are responsive to the opposition presented to the passage of magnetic flux by material passing through the gap.

The invention may be understood more readily by referring to the following detailed description my copending applications S. N. 126,624, iiled Y when considered in connection with the accom- Darwins drawings. The features of my invention which are believed to be novel and patentable are pointed out in the claims appended hereto, or in the claims of my said copending applications. In the drawings, Fig. 1 is a side view, partially in section, of one embodiment of my invention; Fig.2is a sectional view cut by the plane 2-2 of Fig. 1; Fig. 3 is the top view of the apparatus of Figs. 1 and 2 showing a section but by the plane 2-8 of Fig. 1; Fig. 4 is a perspective view of one of the core elements and the face plate of the apparatus of Figs. 1 to 3; Fig. 5 is an electric circuit diagram illustrating schematically the apparatus of Figs. 1 to 4; Fig. 6 is a perspective view of the apparatus arranged for gauging wire; Fig. 7 is a diagram of an alternative electric circuit; Fig. 8 is a diagram representing a foil gauge employing the Wheatstone bridge principle; and Figs. 9 and 10 are diagrams of movable spindle dimension gauges employing the balanced transformer principle oi' Fig. 5. Like reference characters are utilized throughout the drawings to designate like parts.

Referring more in detail to the drawings, the apparatus of Figs. 1 to 7 consists of a fixture Il having a pair .of jaws l2 carrying an electric gauge head l2 with a gap Il therein through which material tovbe gauged is passed. The electric gauge head I3 comprises a laminated ileld structure, windings carried thereon, a source oi' exciting current, and current-responsive apparatus for indicating gauge thickness or foradjusting the sheet-manufacturing apparatus. The eld structure includes an Irl-shaped core element Il with a pair of parallel legs IBV and Il joined by a cross arm Il and a pair of core elements i9 and 20. These core elements may be of U-shape with parallel legs 2i and 22 and 23 and 24, respectively. The legs 2| and 23 are inline with the legs IS of the H-shaped core element II. Likewise, the legs 22 and 2l are in line with the legs Il of the H-shaped core element l5. 'I'he U-shaped elements I9 and 20 are spaced from the H-shaped element I5 to form two pairs of air gaps 25 and 28 between confronting ends of the legs of the elements of the ileld structure.

The pair of air gaps 26 is adapted to have the foil or other sheet material to be gauged pass through, and face plates 21 and 28 made of nonconducting, non-magnetic material are provided to cover the confronting ends of the core elements at the gap-26 for protecting the moving foil against injury as well as providing a pro- The space between the face plates 21 Aand 28 forms the gap I4 within which the sheet material 29 is caused to travel. It will be understood that the direction of travel of the sheet 29 is perpendicular to the plane of the paper in the views of Figs. 1 and 5 and parallel to the plane of the paper in the view of Fig. 2, the sheet, itself, being perpendicular to the plane of the paper in either case.

The H-shaped cere element I carries an exciting Winding 39 on its connecting arm I8, and a source of alternating current 3I is connected to` the exciting winding 30 preferably through a sensitivity-control rheostat or variable imped- 'ance 32. The alternating-current source 3| vis preferably of audio frequency; i. e., below the radio frequency range; for example, it may be a two thousand cycle per second source. For relatively thick materials such as one-sixteenth` inch brass, I have found sixty cycles to be satisfactory. The -U-shaped core elements I9 and 20 carry the detecting windings 33 and 34, respectively, and a current-responsive device, such as a directcurrent milliammeter 35, is indirectly connected to the windings 33 and 34 through a full wave rectifier 36, the connection being such that the windings 33 and 34 are in series opposition with respect to voltages .induced by the exciting winding 39. The rectifier 36 may be of the copper oxide or other suitable type.

In order to operate the rectifier 36 in the range where it operates most eiiiciently and accurately as a rectifier the apparatus is arranged so that current flows in the rectifier 36 for a zero reading of the instrument 35. For this purpose, the

instrument 35 may be made a suppressed zero instrument; but then a uctuation in the supply voltage 3I results in shifting of the zero. In order to avoid the use of a suppressed zero instrument and to prevent zero shift regardless of voltage fluctuations, I supply an opposing current to the instrument 35, which uctuates with the supply voltage. For example, a second full wave rectifier 31 may be provided with its input side energized by the source 3II and with the out, i

put side connected to the instrument 35 in shunt with the output side of the rectifier 36but with polarity reversed with respect to the instrument 35. A transformer 38 is preferably provided for stepping down the input voltage of the rectier 31 to a suitable value and a shunt resistor 39 may be connected across the secondary side of the transformer 38 to make the transformer loading and output voltage relatively independent of variations in instrument current. If desired, a rheof stat 40 may be provided in the secondary circuit of the transformer 38 for adjusting the output current of the rectier 31 to'the best value and adjusting the instrument zero. My invention is not limited to specific numerical values but in the case of rectiers of the output usually employed in connection with milliammeters, I have found two milliamperes to be a suitable value of current output for the rectiers 36 and 31 when the instrument 35 reads zero.

The apparatus may be arranged either as a null device or as a direct indicating device. In

' either case means are provided for balancing the 1 electrical circuit when a sheet of some thickness,

assumed to be a standard thickness, is passed through the gap I4. Balance is obtained by providing a resistor 4I having ends 42 and 43 connected to the output ends of the winding 33 and 34' and an adjustable tap connected to the common terminal 44 of the windings 33 and 34. For

providing both ne and coarse adjustment, an intermediate potentiometer 45 may be provided having end terminals connected to a pair of coarse-adjustment taps 46 movable as a unit along the resistor 4I and having a fine-adjustment tap 41 connected to the common terminal 44 of the windings 33 and 34. Preferably, the resistor 4I is provided with contacts spaced to conform to the spacing between the taps 46, e. g. with half the spacing so that the coarse-adjustment taps 46 always bridge two sections of the provided with left and right contacts 49 and 50,

respectively, for energizing suitable controls to increase or decrease the thickness of the sheet being produced. The apparatus for forming or rolling the sheets and the controls therefor do not form a part of my invention,fand, consequently, are not illustrated in the drawings.

In order to protect the parts of the electric gauge I3 against dirt, against magnetic dustand against 'particles of electrically-conducting material, the parts are preferably enclosed by cylindrical cases 15 and 16 closed at the ends by a plate 11 supporting the U-shaped core element I9, by the face plates 21 and 28, and by a base plate 18 resting upon the lower jaw I2 and supporting the lower U-shaped core element 20. The H-shaped core `element I5 is supported by the face plate 21 secured to the cylindrical case 15 and the case 15 is in turn secured to the upper jaw I2 of the fixture I I by a band 19.

The use of audio-frequency as distinguished from high frequency current for energizing the apparatus results in magnetic flux capable of penetrating the foil 29 and makes the readings relatively independent of the surface characteristics of the foil and responsive only to its thickness. The use of audio-frequency current also makes it unnecessary to provide a vacuum-tube or from a reel on which it may beestored through the gap I4 on to a reel upon which it is rerolled. Since the sheet 29 is composed of electricallyconducting material, it opposes the passage of ux across the pair of air gaps 26 and the `strength of the opposition to flux depends upon the thickness of the material 29.' The windings 30 and 34 form the primary and secondary windings, respectively, of a transformer of which the transformer ratio is varied by the opposition to ux passage produced by the sheet 29. The detecting winding 33 also forms a second secondary winding of the transformer and a variation in the opposition to ux produced by the sheet 29 varies the relative magnitudes of the voltages induced in the windings 33 and 34. Since the windings 33 and 34 are oppositely connected to the portions of the resistor 4I above and below the tap 41, the input to the rectified depends upon the difference between the voltage drops in the portions of the resistor 4I above and below the tap 41, and this difference depends upon variations in foil thickness and the setting of the taps 41 and 46. If the apparatus is balanced to give a zero reading for a given Astandard foil thickness by placing a foil of standard thickness in the gap 26 and adjusting the taps 45 and 41 until the instrument 35 reads zero, the instrument will thereafter read in terms of'deviation from standard thickness. Variations in voltage of V the supply source 3I will not affect the zero setting because the equal current outputs of the rectifiers 36 and 31 will be affected in the same proportion. Voltage fluctuations will, however, affect the sensitivity. In order to check the sensitivity, after the zero has been checked, a foil of known deviation from standard is placed ln the gap 26 and the rheostat 32 is adjusted until the correct reading is given by the instrument 35. For reasons already explained adjustment of the rheostat 32 will not disturb the zero adjustment.

In case of application of my invention in an automatic foil rolling mill, deviations from the desired thickness of 'foil will vary the opposition to flux crossing the pair of air gaps 26. varylng/ the voltage induced in the windings 34 and -un-` balancing the voltages appearing in the secondary windings, thereby producing. a reading in the instrument 35 and operating the relay 43 in whichever direction is required to correct the adjustment of the mill. If desired, of course, the taps 45 and 41 may be so set as to produce a zero deflection of the instrument 35 when no sheet is present in the gaps 26 and the instrument 35 may then be calibrated in terms of the thickness of sheet passed through the gaps 26. In this case, a contact-making milliammeter will be substituted for the directional relay 43 and it will be adjusted to operate at the current corresponding to the desired sheet thickness.

Although I have explained the operation of my ously. For example, as illustrated in Fig. 6, nonmagnetic guide rollers or sheaves 5I may be provided for holding a wire 52 in the form of a loop with a portion 53 passing through the airgap I4 between the legs-IB and I1 of the magnetic core'element I5. An additional roller or sheave 'f 54 is provided which is composed of material which is non-magnetic but which serves as a good conductor of electricity. such as copper. Conseouently. an electrically-closed loop of wire is formed, notwithstanding the fact that the wire may travel around the rollers continuously as the wire isl passed through the testing apparatus. It will be understood that suitable arrangementsY are to be provided for keeping the wire 52 taut and maintaining a good contact at the lroller 54. Obviously, the loop of wire 52 reacts upon the magnetic eld of the apparatus and thus permits readings to be obtained of the thickness or purity of the wire, as previously explained, as well as permitting indications of aws, such as cracks or transverse cuts.

An alternative electrical circuit arrangement may be used as illustrated in Fig. '1. Here the windings 33 and 34 are connected aiding instead of in opposition, and the input terminals of the rectifier 36 are connected between the tap 41 and Athe common terminal 44 of the windings 33 and 34. The windings 33 and 34 thus form two arms of a bridge with the upper and lower portions 55 and 55 of theresistor 4I forming two opposite arms. The circuit is balanced as before by adjusting the positions of the coarse and ilne adjustment taps 46 and 41. It is apparent that both in Fig. 5 and in Fig. '1, the windings 33 and 34 are connected in differential or opposed relationship to the rectifier 35 and the instrument 35 and inV both cases a double-mesh circuit arrangement is produced.

If desired, bridge circuits similar to those of my said copending application, Serial No. 198,337, may be used for foil gauging. An example is illustrated in Fig. 8. A bridge is formed by two reactors 51 and 58 and two portions 53 and Il of an impedance 5I connected in series parallel to the alternating-current source 3|. The reactor 51 has air gaps 25 through which the foil to be gauged may pass. The impedance 6I may be provided with an adjustable tap 52 for varying the relative impedances of the arms 59 and 3l of the bridge for balancing purposes or a rheostat 63 shunting one of the reactances 51 or 58 may be provided. The input terminals of the rectifier 36 are connected between the tap 62 and a point 64 forming the common terminal of the reactances 51 and 58. Variations in foil thickness will cause variations in the degree of imbalance of the bridge consisting of arms 51,

5s. ss and so and the instrument 3s may be' calibrated in terms of foil thickness.

If the transformer primary 30 and its core I5 of Fig. 5 are made movable and connected to the movable spindle of a dimension gauge such as that disclosed in my said copending application 198,337, the differential output of the transformer secondaries 33 and 34 will represent deviations from a standard dimension. The secondaries may be connected either in parallel opposition as in Fig. 7, or in series opposition as in Figs. 5 or 9. In Fig. 9 is shown the movable spindle 65 of a dimension 'gauge having an anvil 55 upon which an object 61 to be gauged may be placed so that the thickness of the object 51 is measured byv determining the position of the spinde 65. The spindle 65 carries a transformer core 63 upon which the primary coil 33 is wound. The tip 69 of the core 68 is positioned between the ends of the cores I 9 and 2|! of the secondary windings 33 and 34, which, in this embodiment. are directlyconnected in series opposition to the input lside of the rectifier 35. Thecores I9 and 20 are supported in a suitable manner by the stationary part of the apparatus (not shown). Preferably the spindle 65 is resilient-ly mounted as by means of leaf springs 10 supported by stationary blocks 1I. The spindie 65. springs 11|v andblocks 1I are composed of magnetiza'ble material to form two parallel branch magnetic circuits for the flux induced bythe primary winding 30. The relative magnitudes of the air gaps 25 and 26 of the transformer ratios. and of the voltages of windings 33 and Y 34, depend upon the position of the spindle 55.

Accordingly. the reading of the instrument 35 depends upon the thickness of the test object or as to be always unbalanced in a given direction since the rectifier 36 makes the instrument 35 unresponsive to reversal in direction of unbalance.

In Fig. a modied dimension gauge is shown 1n which a pair of primary windings 12 and 13 are wound upon the stationary cores IS and and a secondary winding 14 is wound upon the movable core 68. The windings 12 and 13 are connected in series and so wound as to pass ux in the same direction through the cores I9 and 20. The secondary winding 'M is connected to the input side of the rectier 36. When the core 68 is centered between the cores I9 and 20 there will be no tendency for flux to flow through the core 68, but when the core 68 departs from this position the magnetic circuits will become unbalanced causing flux to flow through the core 68 and a voltage to be induced in the secondary winding 14. In this case the differential action takes place in the magnetic circuit instead of in the electrical circuit as in the previously illustrated embodiments.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principle and showing its application, but it will be obvious to those skilled in the art that many modicaticns and variations are possible and I aim, therefore, to cover all such modifications and variations as fall within the scope of my invention which is defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A gauge comprising a pair of current-conducting elements, means for producing alternating potential dierence in said elements, means for .producing variations in the relative values of the potential differences in response to variations in a quantity to be measured, a rectiiler having a pair of input terminals and a pair of output terminals, said current-conducting elements being connected in diierential relationship to said input terminals, a direct-currentresponsive device connected to said output terminals, and means for supplying a direct voltage to said current-responsive device of opposite polarity to that supplied by the output terminals of said rectier and of suicient magnitude to maintain the current in the rectifier sufficiently high for accurate operation as a rectier.

2. A foil thickness gauge comprising in combination a magnetic core element with branches forming parallel magnetic circuits, an exciting winding in inductive relation to both of said magnetic core branches, at least one-of said magnetic core branches including an air gap adapted for passage of foil to be gauged, an impedance element having an adjustable tap, a detecting winding linking one of said core branches, a second detecting winding linking the other of said core branches, said detecting windings being connected in series opposition across said impedance element with a common terminal connected to said tap, a rectier having input terminals connected across said impedance element and having Aoutput terminals, a second rectifier having input and output terminals, means for maintaining proportionality of voltage across said latter input terminals and the said exciting winding, and a direct-current-responsive device to which said rectier output terminals are connected in opposed relation. Y

3. A foil thickness gauge comprising in compiece 61. Preferably the apparatus is so adjustedv bination a magnetic core element with branches forming parallel magnetic circuits, an exciting winding in inductive relation to both of said magnetic core branches, at least one of said magnetic core branches including an air gap adapted for passage of foil to be gauged, a resistor having an adjustable tap, a detecting wind-- ing linking one of said core branches, a second detecting winding linking the other of said core branches said detecting windings being connected in series opposition across said resistor with a common terminal connected to said tap,

`- a rectier having input terminals connected magnetic circuits being in diierential relationship to the windings with respect to the output Aelectric connections, a rectier having a pair of input terminals connected to said output electrical connections and having a pair of output terminals, a direct-current-responsive device connected to said rectier output terminals and means for supplying a direct voltage of opposite polarity to that Supplied to the output terminals of said rectier and of suiiicient magnitude to maintain the current in the rectifier sufliciently high for accurate operation as a rectier.

5. A foil thickness gauge comprising in combination a magnetic core element with branches forming parallel magnetic circuits, an exciting winding in inductive relation to both of said magnetic core branches, at least one of said magnetic core branches including an air gap adapted for .passage of foil to be gauged, a current-carrying impedance element having an adjustable tap, a detecting Winding linking one of' said core branches, a second detecting winding linking the other of said core branches, said detecting windings being connected in series aiding across said impedance element, a rectifier `having input terminals connected to the common terminal of said detecting windings and said ltap respectively, and having output terminals,

. said input terminals dependent in magnitude upon the relative values of said potential differences. a direct-current-responsivedevice connected to said output terminals, and means for supplying a direct voltage to said current-responsive device of opposite polarity to vthat supplied by the output terminals of said rectifier and of suicient magnitude to maintain the cu.-

rent-carrying impedance element in series with.

said reactor, a pair of impedances connected in l series, a rectifier having a pair of input terminals,

one of which is connected to the common point of said reactor and said current-carrying impedance element, and the other of which is connected to the common point of said pair of impedances, a pair of terminals to which thenseries connected elements are connected to form a Wheatstone bridge'circuit, a current responsive instrument connected to the output terminals of said rectiiier, a second rectiferhaving input and output terminals, the output terminals being connected' to the output terminals of the rst rectifier but with reverse polarity,. means for maintaining Yproportionality of potential difference between the input terminals of said Wheatstone bridge and the input terminals of said second rectiiier.

8. A foil thickness gauge comprising in combination a reactanceelement having a core with an air gap adapted for passage of foil to be forms the diagonal arm of a. Wheatstone bridge circuit, and a source for supplying a direct voltage to said current responsive device of oppositev polarity to that supplied by the output terminals of said rectifier and of suficient magnitude to maintain the current in the rectifier sumciently high for accurate operation as a rectier.

9. A foil thickness gauge comprising in combination a magnetic core element with branches forming parallel magnetic circuits, an exciting .winding in inductive relation to both of said branches, said detecting windings being congauged, and three impedance elements, the forey nected across said resistor and having a common terminal, a rectifier having input terminals and output terminals, connections between the common terminal of said detecting windings and an intermediate point on said resistor to form two mesh circuits, the input'terminals of said rectier being connected in differential relationship to said mesh circuits, a direct current responsive device connected to said output terminals, and means for supplying to said direct current responsive device a current having a polarity opposite to that supplied by the output terminals of the rectiiier and of suiiicient magnitude to maintain the current in the rectifier suiiiciently high for accurate operation asA a rectifier.

CLAUDE M. HATHAWAY. 

